Discrimination of tonal patterns with several levels of stimulus uncertainty.

The discrimination of word-length tonal patterns has previously been shown to be strongly dependent on the level of stimulus uncertainty of the psychophysical procedure employed [Watson, Kelly, and Wroton, J. Acoust. Soc. Am. 60 (1976)]. An experiment was conducted to determine the range of stimulus uncertainty effects and the time course of discrimination training, under various levels of stimulus uncertainty. Listeners were taught to detect differences between tonal patterns using a three-alternative, forced-choice adaptive psychophysical procedure. The differences to be detected were increments in frequency, level, or duration of one of four target tones whose frequency, duration, intensity, and temporal position were constant in the standard patterns. Asymptotic discrimination performance for the 45-ms target tones presented in the context of a temporal sequence of ten tones with a total duration of 450-ms, ranged from mean threshold values of ΔI, ΔT, ΔF of 13 dB, 40 ms, and 1100 Hz, respectively, under the highest levels of stimulus uncertainty, to levels only slightly greater than those measured for the target tones in isolation. [Work supported by a Biomedical Research Development Grant from NIH.] [ABSTRACT FROM AUTHOR]